Molding is a process by virtue of which a molded article can be formed from molding raw material by using a molding system. Various molded articles can be formed by using the molding process, such as an injection molding process. One example of the molded article that can be formed, for example, from polyethylene terephthalate (PET) material is a preform that is capable of being subsequently blow-molded into a beverage container, such as, a bottle and the like. Other examples of the molded articles include thin-wall containers (i.e. yogurt containers, cups, etc), medical appliances and the like.
PET has received wide acceptance for producing various molded articles, including packaging containers, beverage packaging containers, medical appliances and other numerous molded articles. However, PET as molding raw material still suffers from some drawbacks that may be restrictive to further expansion of the areas of applicability of PET. For example, PET has tendency to degrade and generate acetaldehyde when it is heat-processed. Several factors are known to negatively affect occurrence and amount of the generated acetaldehyde, such as: pressure levels, extruder speeds, shear levels, residence time and the like. A molecule of the acetaldehyde is comparatively smaller vis-à-vis the molecule structure of the PET and due to this size disparity, the molecule of acetaldehyde can migrate through the PET to the interior of the molded article and a substance that is eventually maintained within the molded article (such as, for example, a beverage and the like).
Generally speaking, the taste of the acetaldehyde can be categorized as “fruity”. Even though acetaldehyde is a natural occurring flavourant in certain fruits; for many types of food products and beverages, the taste of so-migrated acetaldehyde may be detrimental. For example, presence of such fruity flavor may not be noticed or, if noticed, not considered to be a nuisance when consuming an orange juice beverage or another strongly flavored beverage. However, presence of such fruity flavor may not be well accepted when consuming a spring water beverage, the taste of which is supposed to be “clean” and “natural”. Accordingly, for certain molded articles produced from PET for certain applications the acceptable threshold for the migration of acetaldehyde molecules (and the associated taste) from the molded article into the food or beverage item maintained therein will be much lower.
It is worthwhile noting that acetaldehyde can be produced during different stages of a processing life cycle of the PET material: (a) when PET is synthesized and PET granules are initially prepared, (b) when PET granules are re-heated during plasticizing while manufacturing preforms, (c) when the preforms are reheated for blow-molding into the final shape container.
Several methods have been proposed to decrease the content of acetaldehyde in the molded articles, the so-proposed method targeting one or more of the above-described processing life cycle stages of the PET material
U.S. Pat. No. 7,041,350 issued to Rule et al. on May 9, 2006 discloses a polyester composition with reduced acetaldehyde concentration comprising polyester, at least one hydrogenation catalyst, and at least one source of reactive hydrogen. A method for making the polyester composition is also disclosed along with polyester articles made with the polyester composition. Suitable articles include containers such as bottles. A packaged beverage comprising a container made with the polyester composition is disclosed.
US patent application 2002/0094402 published on Jul. 18, 2002 by Jen discloses a manufacturing method of copolyester for low acetaldehyde content of PET bottles. The polyethylene terephthalate (PET) polymer is added with an appropriate modifier in order to decrease the production of acetaldehyde caused by pyrolysis side reaction during the blow molding process of PET bottles. The modifier comprises stabilizer and primary antioxidant, wherein the stabilizer is an inorganic phosphorous compound with an addition quantity of 0.003˜0.5 weight % based on the weight of the total copolyester copolymer and the primary antioxidant is a hindered phenolic antioxidant containing Ca+2 with an addition quantity of 0.005˜5.0 weight % based on the weight of the total copolyester copolymer. The present invention owns an improving effect of decreasing the production of side product—acetaldehyde at least 30% than those without the addition of said modifier.
U.S. Pat. No. 6,344,166 issued to Aoki, et al. on Feb. 5, 2002 discloses a container molding method for decreasing the amount of released acetaldehyde. The method comprises a primary blow molding step of stretch-blow-molding a preform into a primary blow-molded article; an acetaldehyde decreasing step of decreasing the amount of acetaldehyde released from the primary blow-molded article; and a final blow molding step of stretch-blow-molding the primary blow-molded article having a reduced amount of acetaldehyde into a final container. The primary blow molding step molds the primary blow-molded article which is larger in size than the final container and which has an average wall-thickness of a stretched barrel portion equal to or less than 0.3 mm, that is smaller than the average wall-thickness of a barrel portion of the final container. The acetaldehyde decreasing step heats the thin-walled barrel portion of the primary blow-molded article at a high temperature for a relatively short time. As a result, the final container having a reduced amount of acetaldehyde released from the inner wall of the final container will be molded.